Need Help Jailbreaking

[JoesRoosens]

Hi,

Today I bought an iPhone 3GS from a friend but I got a little confused trying to jailbreak and unlock it. It's an iPhone 3GS, the serial number contains MC (read somewhere this is important), and it's currently on iOS 4.2 (my friend updated it just before selling it) and has modem firmware 5.14.02 It has never been jailbroken/unlocked before.
Anyone know any detailed instructions on jailbreaking and unlocking this device? (probably starting with downgrading) I don't have an official compatible SIM card so it needs to be able to 'hacktivate' (correct?). I still have my regular cellphone so it's not an issue if it's not a phone (although that would be nice) but I'be be very happy if I would be able to use it as an iPod Touch.

I tried downgrading using a guide I found online but kept hitting the "device not eligible for requested build" -error (tried editing hosts file in /etc but without success)

Any help would be very much appreciated!

Joes

[iYeow]

Your baseband cannot be unlock. You use Redsn0w 0.9.6b5 to install Cydia, update ipad baseband, install bundle to jailbreak at 4.2.1 but it will be tethered if you have the new bootrom. If you have the old bootrom , then it will be untethered.
One thing you must note : once you have installed ipad bb, you will not be able to use future stock firmware updates, only custom firmwares.